This invention relates to improvements in systems for measuring the ballistics of a projectile, such as a bullet.
A projectile of a given mass traveling at a given velocity carries a specific amount of kinetic energy [1/2 (Mass)(Velocity).sup.2 ] which is transferred to a target upon impact. Projectiles are readily weighed when at rest thereby facilitating the derivation of mass, and velocity is readily derived using a chronograph or other techniques. However, while mass and velocity are easily measured for a given projectile, the destructive characteristics of the projectile upon impact with a target, and more specifically the destructive characteristics of bullets, vary greatly depending upon the projectile's design and construction.
Two bullets of the same mass and velocity have identical kinetic energies, but depending upon the specific design and construction of the individual bullets they can have vastly different destructive characteristics. A projectile's destructive characteristics relate to how and when the bullet's kinetic energy is transmitted to its target upon impact. A bullet can be designed to have a "large wound" capacity, meaning that the bullet expands and dissipates its energy rapidly while penetrating very little upon impact, which results in a large wound to the surface of the target. In contrast, a bullet with the same mass and velocity as above can be constructed to change its shape more slowly and penetrate deeply into a target leaving a relatively small channel before expending the majority of its energy. Ballisticians design and construct bullets variably such that the majority of their kinetic energy is expended at desired variable predetermined depths upon impact with a target. The shape of the wound cavity in a target typically has a maximum diameter and specific shape which directly corresponds to the bullet's dissipation of energy.
Game hunters think of bullets in relation to their killing power, which can be defined as the bullet delivering an effective destructive force to significant vital organs of the target causing bodily functions to cease. Accordingly, of great interest to ballisticians is at what depth the majority of the energy of a bullet is dissipated, and the shape of the wound cavity. For example, a bullet whose energy is dissipated quickly upon impact ("large wound" capacity) will be relatively ineffective for causing significant damage to the vital organs of a deer or other large animal. However the same "large wound" capacity bullet will be highly effective for killing a squirrel because the depth of penetration required to strike vital organs is relatively shallow. In contrast, a small channel bullet whose maximum kinetic energy is delivered at a deeper depth will be highly effective for damaging the vital organs of a larger animal, such as a deer, and thereby has a high killing power in relation to that animal. The same small channel bullet, when used to kill a squirrel, will probably result in the squirrel's death but will emerge from the squirrel retaining most of its kinetic energy enabling the bullet to strike or ricochet into unintended targets. Ballisticians, with proper design and construction, can control the desired characteristics of energy dissipation of bullets to create highly effective bullets for their intended targets.
To test various bullet and other ordnance designs, ballisticians previously have relied upon a variety of devices and mediums, such as those shown in the following U.S. Pat. Nos.: 523,510; 2,696,105; 2,812,660; 3,024,645; 3,718,041; 4,479,378; and 4,817,960. Ordnance gelatin, which is primarily water, is the standard test medium and currently is widely used by ammunition and bullet makers, including the government, for attempting to determine the ballistic qualities of a given bullet. Gelatin and other mediums in current use are typically time-consuming to use and the information provided by them is sketchy at best. Ordnance gelatin, for example, must be mixed and allowed to gel in a special mold. Temperature is critical and each batch of gelatin must be calibrated and certified immediately prior to use. There is a limited time frame that the gelatin is of the proper consistency for testing ballistics. After discharging a bullet into the gelatin, most of the potentially useful information must be derived from the recovered bullet. Such desired information may include retained weight, frontal diameter and depth of penetration. A severe limitation with the gelatin approach is that the destructive cavity created in the gelatin, which relates to its energy dissipation, is temporary and collapses as the bullet passes through. Attempting to remedy this deficiency, ballisticians have employed burdensome and expensive high-speed cameras to record what occurs as the bullet passes through the medium. Although an improvement, high-speed cameras lack the precision necessary to determine accurately the energy dissipation and other information that would be desirable as the bullet passes through the medium. Further, after each test the bullet must be carefully dug out of the gelatin mold and a new block of gelatin molded. Ideally a ballistic testing system should use a low-cost medium that does not have to be reformed after each use so numerous tests can be performed in rapid succession. Further, a system should provide accurate information of the energy dissipation as a projectile passes through the medium and allow the projectile to be easily recoverable.
Another prior method of obtaining projectile information has been the installation of a strain gauge on a gun barrel to record strain during firing. However, this method produces no information regarding energy dissipation after a bullet leaves the barrel and strikes a target.